In synthesizing optically active amine compounds, heretofore, there have conventionally been employed, for example, the procedure which comprises the use of a naturally occurring amine compound and the method which involves synthesizing a racemic amine, followed by optical resolution with use of an optically active carboxylic acid, and the like. However, the former procedure encounters difficulties in obtaining or procuring the starting compounds, while the latter method has left unsolved the inconvenience that optical resolution fails to produce the desired compound in amounts in excess of those being present prior to such chemical resolution. In order to solve such problems, in recent years, extensively intensified investigation has been conducted into a method for synthesizing optically active amines through catalytic asymmetric hydrogenation of imines. For example, there have been known the methods in which a rhodium complex is used (for example, refer to J. Chem. Soc., Chem. Commun., 1991, pp. 1684), a ruthenium complex is utilized (for example, refer to Inorg. Chem. Acta, 1994, vol. 222, pp. 85), and the like. Nevertheless, it has been pointed out that such synthetic methods suffer individually from the defects or disadvantages, for example, that rhodium metal used is costly, that even when use is made of ruthenium metal being relatively cheaper than rhodium metal, the ruthenium complex as prepared therefrom is somewhat unstable, while the resultant amine shows a not so much enhanced degree of optical purity, and the like. There were published the research papers reporting that relatively less costly iridium metal is utilized, but in such cases, additives are required to be added in order to produce the highly active catalysts (for example, refer to Angew. Chem. Int. Ed. Engl., 1990, vol. 29, p. 558 and Chem. Lett., 1995, p. 955). Although some research reports were also published on the iridium complexes as prepared without use of additives (for example, refer to J. Am. Chem. Soc., 1990, vol. 112, p. 9400 and Chem. Eur. J., 2004, vol. 10, p. 267), there is confronted the problem that such complexes may merely produce the amines with a lowered degree of optical purity, depending upon the type of substrates used.
It was also reported that when an iridium-carboxylate complex catalyst is used in the asymmetric hydrogenation of imines, optically active amine compounds may be produced in high stereoselectivity and yield, even without use of additives (for example, refer to JP 11-335334-A, Proceedings of the 51st Annual Forum on Complex Chemistry, 327 (2a-A07)(Sept. 28 to 30, 2001), Proceedings I of the 81st Spring Meeting of Chem. Soc. of Japan, 499 (IPB-059) (Mar. 26 to 29, 2002) and Proceedings of Molecular Chirality-2002, 47 (PS-3) (Jun. 6, 2002)). However, there is arisen the problem that even use of such complex results in lowered catalytic activity, although this depends upon the type of substrates used.